The present technology relates to a secondary battery-use active material capable of inserting and extracting an electrode reactant, to a secondary battery-use electrode and a secondary battery that use the secondary battery-use active material, and to a battery pack, an electric vehicle, an electric power storage system, an electric power tool, and an electronic apparatus that use the secondary battery.
Electronic apparatuses such as a mobile phone and a personal digital assistant (PDA) have been widely used, and it has been demanded to further reduce the size and the weight of the electronic apparatuses and to achieve their long life. Accordingly, as an electric power source for the electronic apparatuses, a battery, in particular, a small and light-weight secondary battery capable of providing high energy density has been developed.
In these days, it has been considered to apply such a secondary batter not only to the foregoing electronic apparatuses, but also to various applications. Examples of such other applications may include a battery pack attachably and detachably mounted on the electronic apparatuses or the like, an electric vehicle such as an electric automobile, an electric power storage system such as a home electric power server, and an electric power tool such as an electric drill, and various applications other than the foregoing applications are considered.
Secondary batteries utilizing various charge-discharge principles to obtain a battery capacity have been proposed. In particular, a secondary battery utilizing insertion and extraction of an electrode reactant or a secondary battery utilizing precipitation and dissolution of an electrode reactant has attracted attention, since such a secondary battery provides higher energy density than lead batteries, nickel-cadmium batteries, and the like.
The secondary battery includes a cathode, an anode, and an electrolytic solution. The cathode contains an active material (cathode active material) capable of inserting and extracting an electrode reactant. As the cathode active material, in general, an oxide (lithium composite oxide) containing lithium (Li) and one or more transition metal elements as components is widely used.
Various studies have been made on configurations of cathodes containing cathode active materials according to various purposes. Specifically, in order to improve charge-discharge cycle characteristics, a coat of a metal oxide such as magnesium oxide (MgO) is formed on the surface of a cathode containing a lithium-transition metal composite oxide (LixNi1-yCoyOz) (For example, see Patent Literature 1). In order to improve structural stability and thermal stability of a cathode active material, the surface of the cathode active material (LiA1-x-yBx CyO2: A represents Co or the like, B represents Ni or the like, and C represents Mg or the like) is coated with a metal oxide such as an oxide of magnesium (Mg) (for example, see Patent Literature 2). In order to improve capacity, charge-discharge cycle durability, safety, and the like, lithium-nickel-manganese-M composite oxide (LixNiyMn1-y-zMzO2: M is Fe or the like) and lithium-cobalt composite oxide (LixCoO2) are mixed (for example, see Patent Literature 3).
In addition thereto, various studies have been made on configurations of secondary batteries. Specifically, in order to obtain high safety during exposure to high temperature or during storage, lithium bis(fluorosulfonyl)imide (LiFSI) is used as a solvent of an electrolytic solution (for example, see Patent Literatures 4 and 5). In order to easily fabricate an electrochemical system including a polyether/lithium salt electrolyte, a non-solvating polymer and a polar aprotic compound such as sulfamide are used as binders (for example, see Patent Literature 6).
Moreover, various measures have been taken to improve characteristics of secondary batteries. Specifically, in order to improve charge-discharge cycle characteristics and the like, a completed secondary battery is stored in a charged state (for example, see Patent Literatures 7 and 8). In order to manufacture an electrode that is cost effective and environmentally friendly, lithium bis(trifluoro methanesulfonyl)imide (LiTFSI) is contained in an aqueous solution/suspension for electrode formation (for example, see Patent Literature 9). In order to improve reliability in a high-temperature and high-humidity environment, a mixture of a cathode active material (manganese oxide) and an electric conductor is subjected to heat treatment in an organic solvent containing imidazole and LiFSI (for example, see Patent Literature 10). In order to improve decomposition of an electrolytic solution at a high potential, and the like, an electrode is soaked in a pretreatment electrolytic solution in which lithium salt (LiTFSI) is dissolved in an organic solvent containing a nitrile compound, and then a positive voltage is applied to the electrode in such an soaked state (for example, see Patent Literature 11). In order to improve cycle characteristics and the like, an electrolytic solution contains LiTFSI (for example, see Patent Literatures 12 and 13).